Electrolyte and electrochemical device

Abstract

The invention relates to an electrolyte and an electrochemical device. The electrolyte comprises an electrolyte, an organic solvent and an additive, wherein the additive comprises a compound A and a compound B; the compound A has a structure: # imgabs0 #, wherein R1 to R5 are independently selected from a hydrogen atom, a halogen atom, a halogenated or unsubstituted C1-C10 saturated alkyl group, a halogenated or unsubstituted C1-C10 saturated alkoxy group, a halogenated or unsubstituted C2-C10 unsaturated alkyl group, and a halogenated or unsubstituted C2-C10 unsaturated alkoxy group; and the compound B is silicate ester. The high-temperature storage performance and the cycle performance of the battery can be improved through multi-aspect effects and synergistic cooperation of the compound A and the compound B. According to the lithium ion battery adopting the electrolyte, the capacity retention rate and the thickness swelling rate can be remarkably improved under a high-temperature cycle condition and a high-temperature storage condition.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and in particular to an electrolyte and an electrochemical device. Background Art

[0002] The electrolyte is a key component in lithium-ion batteries. Its function is to separate the positive electrode and the negative electrode and provide a conductive channel for lithium ions between the positive and negative electrodes. The electrolyte has an important impact on the energy density, power density, cycle life, safety performance and other aspects of the battery. For example, lithium ions in the electrolyte are prone to excessive deposition in local areas of the negative electrode to form lithium dendrites, which may cause the battery to short circuit. For example, the contact between the electrolyte and the negative electrode in a high temperature environment can easily cause the electrolyte to reduce and produce gas at the negative electrode. The above problems will all lead to reduced battery cycle performance, and these problems need to be solved through breakthroughs in electrolyte research and development. Summary of the invention

[0003] Based on this, it is necessary to provide an electrolyte and an electrochemical device to improve the battery cycle performance.

[0004] The first aspect of the present invention is to provide an electrolyte, the scheme is as follows:

[0005] An electrolyte comprising an electrolyte, an organic solvent and an additive, wherein the additive comprises a compound A and a compound B;

[0006] Wherein, the compound A has a structure shown in formula (1),

[0007]

[0008] In formula (1), R1 to R5 are independently selected from a hydrogen atom, a halogen atom, a halogenated or unsubstituted C1 to C10 saturated alkyl group, a halogenated or unsubstituted C1 to C10 saturated alkoxy group, a halogenated or unsubstituted C2 to C10 unsaturated alkyl group, or a halogenated or unsubstituted C2 to C10 unsaturated alkoxy group;

[0009] The compound B is a silicate.

[0010] In one embodiment, in formula (1), R1-R5 are independently selected from hydrogen atom, fluorine atom, chlorine atom, bromine atom, halogenated or unsubstituted C1-C3 saturated alkoxy group, halogenated or unsubstituted C2-C3 unsaturated alkyl group, halogenated or unsubstituted C2-C3 unsaturated alkoxy group.

[0011] In one embodiment, in formula (1), R1~R5 are independently selected from hydrogen atom, fluorine atom, halogenated or unsubstituted C1~C3 saturated alkyl group, fluorinated or unsubstituted C1~C3 saturated alkyl group, fluorinated or unsubstituted C1~C3 saturated alkoxy group, fluorinated or unsubstituted C2~C3 unsaturated alkyl group, fluorinated or unsubstituted C2~C3 unsaturated alkoxy group; at least one of R1~R5 is fluorine atom and / or at least one fluorinated C1~C3 saturated alkyl group.

[0012] In one embodiment, the compound A is selected from at least one of the following compounds:

[0013]

[0014]

[0015] In one embodiment, the compound B is selected from at least one of tetraethyl orthosilicate, ethyltriacetoxyethylsilane, and methyltriacetoxysilane.

[0016] In one of the embodiments, in the electrolyte solution, the concentration of the electrolyte is 0.5 mol / L to 1.5 mol / L.

[0017] In one embodiment, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0018] In one of the embodiments, in the electrolyte, the mass fraction of the compound A is 0.5% to 10%, and the mass fraction of the compound B is 0.1% to 5%.

[0019] In one embodiment, the additive further includes at least one of fluorocarbonate and nitrile compounds.

[0020] In one of the embodiments, the mass fraction of the fluorocarbonate is 5% to 35%, and the mass fraction of the nitrile compound is 1% to 7%.

[0021] In one embodiment, the fluorocarbonate includes at least one of ethylene fluorocarbonate, methyl ethyl fluorocarbonate, and diethyl fluorocarbonate.

[0022] In one embodiment, the nitrile compound includes at least one of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, 1,2,3-tri(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tri(cyanoethoxy)pentane.

[0023] The second aspect of the present invention is to provide an electrochemical device, the scheme is as follows:

[0024] An electrochemical device comprises a housing, a positive electrode sheet, a negative electrode sheet, a diaphragm and the electrolyte described in any one of the above embodiments arranged in the housing.

[0025] Compared with conventional technologies, the above electrolyte and electrochemical device have the following beneficial effects:

[0026] Compound A and compound B are added to the above electrolyte. In the first charge and discharge formation stage, compound A is first reduced to form an SEI film at the negative electrode, forming a better lithium-philic inner layer structure, which can induce the uniform distribution and diffusion of lithium ions on the surface of the negative electrode, avoid excessive deposition of lithium ions in local areas to form lithium dendrites, thereby reducing the risk of battery short circuit, and effectively improving the cycle performance of the battery. The fluorine-containing compound A enables the electrolyte to more evenly infiltrate the surface of negative electrode materials such as graphite, avoiding abnormal lithium ion transmission under high-density battery design. At the same time, compound A can also improve the reversibility of the electrolyte on the negative electrode side. Specifically, compound A has lipophilic groups, such as hydrocarbon groups of aromatic, ester, ether, amine, amide and other groups, which can be adsorbed on the surface of negative electrode materials such as graphite, while the negatively charged hydrophilic groups can adsorb positively charged ions in the electrolyte, making these ions easily enriched on the surface of the negative electrode, reducing the concentration polarization in the electrolyte at the negative electrode, and promoting the electrochemical reaction. Compound B can form a protective layer on the surface of the negative electrode, which can improve the structural stability of the negative electrode, especially the cycle stability under high current density, thereby extending the service life of the battery. At the same time, under a specific high temperature environment, compound B can also be induced to undergo a polycondensation reaction and form a polymer network with good thermal stability, thereby achieving passivation of the graphite negative electrode, reducing the contact between the electrolyte and the negative electrode under high temperature conditions, preventing the electrolyte from reducing and producing gas on the negative electrode, and improving the high temperature storage performance and high temperature cycle stability of the battery.

[0027] The high temperature storage performance and cycle performance of the battery can be improved through the multi-faceted effects of compound A and compound B. The lithium-ion battery using the above electrolyte can achieve outstanding improvement in capacity retention and thickness expansion under high temperature cycle conditions and high temperature storage conditions.

[0028] The electrochemical device described above has the electrolyte described in any of the above embodiments, and thus has corresponding technical features and can achieve corresponding beneficial effects. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0031] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0032] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0034] The term "saturated alkyl" refers to a saturated hydrocarbon containing primary carbon atoms, secondary carbon atoms, tertiary carbon atoms, quaternary carbon atoms, or a combination thereof. Phrases containing this term, such as "C1-C 10 "Alkyl" refers to an alkyl group containing 1 to 10 carbon atoms, and each occurrence can be independently C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl or C 10Alkyl. The alkyl group may be straight-chain or branched. Suitable examples include, but are not limited to, methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(C H3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (- CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl (-CH2CH2CH2CH2CH2CH3), 2-hexyl (-CH(CH3)CH2CH2CH2CH3), 3-hexyl (-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl (-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (-CH(CH3)CH( 2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl (-(CH2)7CH3).

[0035] The term "unsaturated alkyl group" refers to a group having at least one carbon-carbon double bond or at least one carbon-carbon triple bond, compared to a "saturated alkyl group".

[0036] The term "saturated alkoxy" refers to a group having an -O-alkyl group, i.e., an alkyl group as defined above connected to a parent core structure via an oxygen atom. Phrases containing this term, for example, "C1-C 10 "Alkoxy" means that the alkyl portion contains 1 to 10 carbon atoms and each occurrence can be independently C1 alkoxy, C4 alkoxy, C5 alkoxy, C6 alkoxy, C7 alkoxy, C8 alkoxy, C9 alkoxy or C 10Alkoxy. The alkoxy group may be straight chain or branched. Suitable examples include, but are not limited to, methoxy (-O-CH3 or -OMe), ethoxy (-O-CH2CH3 or -OEt) and tert-butoxy (-OC(CH3)3 or -OtBu).

[0037] The term "unsaturated alkoxy" refers to a group having at least one carbon-carbon double bond or at least one carbon-carbon triple bond, compared to a "saturated alkoxy".

[0038] "Halogen" or "halo" refers to F, Cl, Br or I.

[0039] The invention provides an electrolyte.

[0040] The electrolyte of one embodiment includes an electrolyte, an organic solvent and an additive, wherein the additive includes a compound A and a compound B.

[0041] Wherein, compound A has the structure shown in formula (1),

[0042]

[0043] In formula (1), R1 to R5 are independently selected from a hydrogen atom, a halogen atom, a halogenated or unsubstituted C1 to C10 saturated alkyl group, a halogenated or unsubstituted C1 to C10 saturated alkoxy group, a halogenated or unsubstituted C2 to C10 unsaturated alkyl group, and a halogenated or unsubstituted C2 to C10 unsaturated alkoxy group.

[0044] Wherein, compound B is a silicate.

[0045] The electrolyte contains compound A as an additive. Compound A can form a protective and lithium-philic SEI film at the positive electrode and the negative electrode, and has a good film-forming effect.

[0046] In terms of the positive electrode, when using battery positive electrode materials such as ternary high-nickel materials (such as NCA, NMC, etc.), the high nickel content in the high-nickel ternary materials brings about the problem of structural instability. At the same time, the 4-valent nickel ions in the high nickel have high catalytic activity and are easy to destroy the electrolyte structure. The compound A in the above electrolyte forms an SEI film at the positive electrode, which can promote the transmission of lithium ions between the positive electrode and the electrolyte, and help improve the battery's charge and discharge efficiency and cycle performance. At the same time, the SEI film formed can protect the positive electrode, improve the stability of the positive electrode material, reduce the volume change and structural damage of the positive electrode material during the charge and discharge process, and extend the service life of the battery.

[0047] On the other hand, compound A forms a SEI film at the negative electrode, which can induce uniform distribution and diffusion of lithium ions on the surface of the negative electrode, avoid excessive deposition of lithium ions in local areas to form lithium dendrites, thereby reducing the risk of battery short circuit, and can effectively improve the cycle performance of the battery. At the same time, compound A also improves the reversibility of the electrolyte on the negative electrode side. Specifically, compound A has lipophilic groups, such as hydrocarbon groups of aromatic, ester, ether, amine, amide and other groups, which can be adsorbed on the surface of negative electrode materials such as graphite, while the negatively charged hydrophilic groups can adsorb positively charged ions in the electrolyte, making these ions easily enriched on the surface of the negative electrode, reducing the concentration polarization in the electrolyte at the negative electrode, and promoting the electrochemical reaction.

[0048] In some of the examples, in formula (1), R1 to R3 are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a halogenated or unsubstituted C1 to C3 saturated alkyl group, a halogenated or unsubstituted C1 to C3 saturated alkoxy group, a halogenated or unsubstituted C2 to C3 unsaturated alkyl group, and a halogenated or unsubstituted C2 to C3 unsaturated alkoxy group.

[0049] In some of the examples, in formula (1), R1 to R3 are independently selected from a hydrogen atom, a fluorine atom, a fluorinated or unsubstituted C1 to C3 saturated alkyl group, a fluorinated or unsubstituted C1 to C3 saturated alkoxy group, a fluorinated or unsubstituted C2 to C3 unsaturated alkyl group, and a fluorinated or unsubstituted C2 to C3 unsaturated alkoxy group.

[0050] In some of the examples, at least one of R1 to R5 is a fluorine atom and / or at least one fluorinated C1 to C3 saturated alkyl group. The fluorine-containing compound A improves the wetting effect on the negative electrode, allowing the electrolyte to evenly infiltrate the surface of the negative electrode material such as graphite, especially the wetting effect under the high-density and high-area density battery design, avoiding abnormal lithium ion transmission under the high design.

[0051] In some examples, compound A is selected from at least one of the following compounds.

[0052]

[0053] Compound A can be prepared by the following method:

[0054] Compound C and compound D are reacted in the presence of a catalyst.

[0055] Wherein, compound C is trifluoromethanesulfonic anhydride.

[0056] Compound D has the following structure.

[0057]

[0058] The catalyst can be an organic base, such as ethylenediamine.

[0059] The chemical formula of the above reaction is shown below.

[0060]

[0061] In a specific example, compound A is compound (1). Compound (1) can be obtained by reacting trifluoromethanesulfonic anhydride and 2,5-difluorophenol under the catalysis of an organic base ethylenediamine.

[0062] The chemical formula of the above reaction is shown below.

[0063]

[0064] In some of the examples, in the electrolyte, the mass fraction of compound A is 0.5% to 10%. Further, the mass fraction of compound A is 1% to 8%. Further, the mass fraction of compound A is 2% to 6%. In some specific examples, the mass fraction of compound A is, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc.

[0065] Negative electrodes such as graphite may expand and contract in volume during the charging and discharging process, resulting in damage to the material structure and a decrease in performance.

[0066] The electrolyte contains compound B as an additive, which can form a protective layer on the surface of the graphite negative electrode, improve the structural stability of the graphite negative electrode, especially the cycle stability under high current density, thereby extending the service life of the battery. At the same time, under a specific high temperature environment, compound B can also be induced to undergo a condensation reaction and form a polymer network with good thermal stability, thereby achieving passivation of the graphite negative electrode.

[0067] In some of the examples, in the electrolyte, the mass fraction of compound B is 0.1% to 5%.

[0068] The synthesis method of compound B: tetraethyl orthosilicate is synthesized by using silicon tetrachloride and propyl acetate.

[0069]

[0070] Adding compound A and compound B to the above electrolyte can achieve a good composite effect at the negative electrode. In the first charge and discharge formation stage, compound A is first reduced to form an SEI film at the negative electrode, forming a better lithium-philic inner layer structure, which can induce the uniform distribution and diffusion of lithium ions on the surface of the negative electrode, avoid excessive deposition of lithium ions in local areas to form lithium dendrites, thereby reducing the risk of battery short circuit, and can effectively improve the cycle performance of the battery. The fluorine-containing compound A enables the electrolyte to more evenly infiltrate the surface of negative electrode materials such as graphite, avoiding abnormal lithium ion transmission under high-density battery design. At the same time, compound A can also improve the reversibility of the electrolyte on the negative electrode side. Specifically, compound A has lipophilic groups, such as hydrocarbon groups of aromatic, ester, ether, amine, amide and other groups, which can be adsorbed on the surface of negative electrode materials such as graphite, while the negatively charged hydrophilic groups can adsorb positively charged ions in the electrolyte, making these ions easily enriched on the surface of the negative electrode, reducing the concentration polarization in the electrolyte at the negative electrode, and promoting the electrochemical reaction. Negative electrode materials such as graphite may expand and shrink in volume during the charge and discharge process, resulting in damage to the material structure and a decrease in performance. Compound B can form a protective layer on the surface of the negative electrode, which can improve the structural stability of the negative electrode, especially the cycle stability under high current density, thereby extending the service life of the battery. At the same time, under a specific high temperature environment, compound B can also be induced to undergo a condensation reaction and form a polymer network with good thermal stability, thereby achieving passivation of the graphite negative electrode, reducing the contact between the electrolyte and the negative electrode under high temperature conditions, preventing the electrolyte from reducing and producing gas on the negative electrode, and improving the high temperature storage performance and high temperature cycle stability of the battery.

[0071] The high temperature storage performance and cycle performance of the battery can be improved through the multi-faceted effects of compound A and compound B. The lithium-ion battery using the above electrolyte can achieve outstanding improvement in capacity retention and thickness expansion under high temperature cycle conditions and high temperature storage conditions.

[0072] Optionally, the electrolyte may be, but is not limited to, a lithium salt. Preferably, the electrolyte is a lithium salt containing fluorine.

[0073] The lithium salt may be at least one of an organic lithium salt and an inorganic lithium salt. The organic lithium salt is preferably at least one of trifluorosulfonyl lithium, difluoro(trifluoromethylsulfonyl)imide lithium, tri(trifluoromethylsulfonyl)methyl lithium and bis(trifluoroimide)sulfonate lithium. The inorganic lithium salt is preferably at least one of hexafluorophosphate, hexafluoroarsenate and lithium perchlorate.

[0074] The concentration of electrolyte in the electrolyte has an important influence on the performance. If the concentration of electrolyte is too low, the conductivity of the electrolyte is low, which will affect the rate performance and cycle performance of the battery system. If the concentration of electrolyte is too high, the viscosity of the electrolyte will be too high, which will also affect the rate performance of the battery system. Therefore, it is necessary to control the concentration of electrolyte in the electrolyte within an appropriate range.

[0075] For example, in some of the examples, in the electrolyte, the concentration of the electrolyte is 0.5mol / L to 1.5mol / L. The concentration of the electrolyte is within the above range, which enables the battery system to obtain better rate performance and cycle performance. Further, in some of the examples, the concentration of the electrolyte is 0.8mol / L to 1.3mol / L. Further, in some of the examples, the concentration of the electrolyte is 1mol / L to 1.2mol / L. In some specific examples, the concentration of the electrolyte is, for example, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, etc.

[0076] In some of the examples, the mass fraction of the solvent is 10% to 80%. Further, in one of the examples, the mass fraction of the solvent is 40% to 70%.

[0077] Optionally, the organic solvent may be, for example, but not limited to, at least one of a carbonate solvent, a carboxylate solvent, a nitrile solvent, a sulfone solvent, and an ether solvent. In some of these examples, the organic solvent is selected from at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent. Further, in some of these examples, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran. Further, the organic solvent is selected from at least two of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, and tetrahydrofuran.

[0078] In some examples, the additive further includes at least one of fluorocarbonate and nitrile compounds.

[0079] In some examples, the mass fraction of the fluorocarbonate is 5% to 35%, and the mass fraction of the nitrile compound is 1% to 7%.

[0080] In some examples, the fluorocarbonate includes at least one of ethylene fluorocarbonate, ethyl methyl fluorocarbonate, and diethyl fluorocarbonate.

[0081] In some examples, the nitrile compound includes at least one of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tris(cyanoethoxy)pentane.

[0082] Furthermore, the present invention also provides an electrochemical device.

[0083] An electrochemical device according to an embodiment includes a housing, a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte according to any one of the above examples, which are arranged in the housing.

[0084] The electrochemical device mentioned above may be, but is not limited to, a lithium-ion battery or the like.

[0085] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is arranged on the positive electrode current collector.

[0086] Illustratively, the positive electrode current collector includes, for example, but is not limited to, copper foil, aluminum foil, and the like.

[0087] It is understood that the positive electrode active material layer includes positive electrode materials. Exemplarily, the positive electrode materials include, but are not limited to, one or more of lithium nickel manganese cobalt ternary materials, lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4) and lithium manganese oxide (LiMn2O4).

[0088] It is understood that the positive electrode active material layer may further include a positive electrode binder, a positive electrode conductor, etc. Exemplarily, the positive electrode binder includes, but is not limited to, one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, epoxy resin, and nylon. Exemplarily, the positive electrode conductor includes, but is not limited to, one or more of graphite, carbon black, acetylene black, and Ketjen black.

[0089] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is arranged on the negative electrode current collector.

[0090] Illustratively, the negative electrode current collector includes, for example, but is not limited to, copper foil, aluminum foil, and the like.

[0091] It is understood that the negative electrode active material layer includes negative electrode materials. Exemplarily, the negative electrode materials include, but are not limited to, natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 and one or more of Li-Al alloys.

[0092] The positive electrode sheet and the negative electrode sheet can be prepared by mixing and dispersing the corresponding active material, binder and conductive agent in a solvent to obtain a slurry, then coating the slurry on a composite current collector, and then drying to remove the solvent to form a corresponding active material layer on the composite current collector.

[0093] The diaphragm includes a polymer film material. For example, the material of the polymer film material includes one or more of polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer diaphragm or a multi-layer diaphragm.

[0094] The following specific examples are provided to further illustrate the present invention. The present invention provides the following specific examples for a better understanding of the present invention, but is not limited to the specific implementation methods and does not limit the protection scope of the present invention.

[0095] Example 1

[0096] This embodiment provides an electrolyte solution comprising an electrolyte, an organic solvent and an additive, wherein the additive comprises compound A.

[0097] An organic solvent including 10 parts of ethylene carbonate (EC), 10 parts of propylene carbonate (PC), 50 parts of ethyl methyl carbonate (EMC) and 30 parts of diethyl carbonate (DEC) was weighed and mixed uniformly to obtain a mixed solvent.

[0098] Add additives 1,3-propane sultone (PS) 3 parts, fluoroethylene carbonate (FEC) 4 parts, succinonitrile (SN) 1 part, lithium salt additive lithium difluorooxalate borate (LiODFB) 1 part, bis(fluorosulfonyl)imide lithium salt (LiFSI) 2 parts, lithium difluorophosphate (LiPO2F2) 0.5%wt to the above mixed solvent, mix well, add lithium salt lithium hexafluorophosphate (LiPF6), and obtain a mixed solution with a concentration of LiPF6 of 1.2 mol / L. Add compound A (structural formula:

[0099]

[0100] ) 1% and compound B (tetraethyl orthosilicate) 1%, mixed evenly to obtain an electrolyte.

[0101] Example 2

[0102] The electrolyte provided in this embodiment is different from that in Embodiment 1 only in that the structural formula of compound A is:

[0103]

[0104] Example 3

[0105] The electrolyte provided in this embodiment is different from that in Embodiment 1 only in that the structural formula of compound A is: Compound B is ethyltriacetoxysilane.

[0106] Example 4

[0107] The electrolyte provided in this embodiment is different from that in Comparative Example 1 only in that the added amount of compound A is 0.5% and the added amount of compound B is 0.1%.

[0108] Example 5

[0109] The electrolyte provided in this embodiment is different from that in Comparative Example 1 only in that the addition amount of compound A is 5%, and the addition amount of compound B is 2.5%.

[0110] Example 6

[0111] The electrolyte provided in this embodiment is different from that in Comparative Example 1 only in that the addition amount of compound A is 10% and the addition amount of compound B is 5%.

[0112] Comparative Example 1

[0113] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 0.3% and the addition amount of compound B is 0%.

[0114] Comparative Example 2

[0115] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 0.5% and the addition amount of compound B is 0%.

[0116] Comparative Example 3

[0117] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound B is 0%.

[0118] Comparative Example 4

[0119] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 2% and the addition amount of compound B is 0%.

[0120] Comparative Example 5

[0121] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 5%, and the addition amount of compound B is 0%.

[0122] Comparative Example 6

[0123] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 10% and the addition amount of compound B is 0%.

[0124] Comparative Example 7

[0125] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 0%.

[0126] Comparative Example 8

[0127] The electrolyte provided in this comparative example is different from that in Example 1 only in that the addition amount of compound A is 0% and the addition amount of compound B is 0%.

[0128] The components of the electrolytes of the above examples and comparative examples are shown in Table 1.

[0129] Table 1 Composition of the electrolyte of the embodiment and the comparative example

[0130]

[0131]

[0132]

[0133] The electrolytes of the above-mentioned embodiments and comparative examples were used to prepare lithium-ion batteries, and the lithium-ion batteries were prepared according to the following method.

[0134] Preparation of positive electrode:

[0135] Weigh the positive electrode active material NCM, the binder polyvinylidene fluoride PVDF and the conductive agent carbon nanotube CNT in a mass ratio of 97:1.5:1.5, disperse them in NMP (N-methylpyrrolidone) solvent, and stir and mix them thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode collector (aluminum foil), and then dried, cold pressed and other processes are performed to prepare the positive electrode sheet.

[0136] Preparation of negative electrode sheet:

[0137] The negative electrode active material graphite, the binder styrene butadiene rubber, the conductive agent acetylene black and the thickener sodium carboxymethyl cellulose are dispersed in a deionized water solvent at a mass ratio of 95:2:2:1, and are fully stirred and mixed to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector (copper foil), and then dried, cold pressed and other processes are performed to prepare a negative electrode sheet.

[0138] Preparation of lithium-ion batteries:

[0139] Obtain a diaphragm, which includes a PP base layer and a ceramic coating applied on both sides. The positive electrode sheet, diaphragm, and positive electrode sheet prepared above are stacked so that the diaphragm is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging bag, and the dried bare cell is respectively injected with the above electrolyte, and a lithium-ion battery is prepared through vacuum packaging, standing, forming, shaping and other processes.

[0140] The following performance tests were performed on each of the lithium-ion batteries prepared above.

[0141] 1. High temperature cycle test

[0142] Test method: Place the lithium-ion battery in an environment with a temperature of 45±2℃, follow the standard charge and discharge cycle, with a cycle rate of 1C and a charging voltage of 3.0~4.4V, and calculate the capacity retention rate of the battery after the cycle.

[0143] The calculation formula of capacity retention rate is as follows:

[0144] The nth cycle capacity retention rate = (nth cycle discharge capacity) / (first cycle discharge capacity) * 100%

[0145] 2. High temperature storage test

[0146] Test method: At room temperature, charge the lithium-ion battery to 4.4V at 0.5C current, place the fully charged battery at 60℃ for 30 days, and measure the thickness expansion rate. After returning to room temperature, discharge the lithium-ion battery to 3.0V at 0.5C current, and record the discharge capacity.

[0147] The test results are shown in Table 2.

[0148] Table 2 Performance test results of lithium-ion batteries using different electrolytes

[0149]

[0150]

[0151] According to the experimental results, it can be seen from comparative examples 1 to 8 that when the additive A is used at a dosage of 1%, the high temperature cycle performance of the battery is significantly improved, and the thickness expansion is also reduced. According to comparative examples 7 and 8, compound B also has certain improvements on the high temperature storage capacity retention rate and high temperature cycle. It can be seen from the embodiments and comparative examples that when compound A and compound B are used in combination, the high temperature performance can be further improved. At the same time, the different substitutions of fluorine atoms in the structure of compound A will have a certain effect on the performance, but the difference is not large, and the overall high temperature performance is still improved.

[0152] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0153] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. An electrolyte, characterized in that: The invention comprises an electrolyte, an organic solvent and an additive, wherein the additive comprises a compound A and a compound B; Wherein, the compound A has a structure shown in formula (1), In formula (1), R1 to R5 are independently selected from a hydrogen atom, a halogen atom, a halogenated or unsubstituted C1 to C10 saturated alkyl group, a halogenated or unsubstituted C1 to C10 saturated alkoxy group, a halogenated or unsubstituted C2 to C10 unsaturated alkyl group, or a halogenated or unsubstituted C2 to C10 unsaturated alkoxy group; The compound B is a silicate.

2. The electrolyte according to claim 1, characterized in that In formula (1), R1 to R5 are independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a halogenated or unsubstituted C1 to C3 saturated alkyl group, a halogenated or unsubstituted C1 to C3 saturated alkoxy group, a halogenated or unsubstituted C2 to C3 unsaturated alkyl group, and a halogenated or unsubstituted C2 to C3 unsaturated alkoxy group.

3. The electrolyte according to claim 2, characterized in that In formula (1), R1 to R5 are independently selected from a hydrogen atom, a fluorine atom, a fluorinated or unsubstituted C1 to C3 saturated alkyl group, a fluorinated or unsubstituted C1 to C3 saturated alkoxy group, a fluorinated or unsubstituted C2 to C3 unsaturated alkyl group, and a fluorinated or unsubstituted C2 to C3 unsaturated alkoxy group; at least one of R1 to R5 is a fluorine atom and / or at least one fluorinated C1 to C3 saturated alkyl group.

4. The electrolyte according to claim 1, characterized in that The compound A is selected from at least one of the following compounds:

5. The electrolyte according to claim 1, characterized in that The compound B is selected from at least one of tetraethyl orthosilicate, ethyltriacetoxysilane and methyltriacetoxysilane.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The concentration of the electrolyte is 0.5 mol / L to 1.5 mol / L; and / or The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate and tetrahydrofuran.

7. The electrolyte according to any one of claims 1 to 5, characterized in that In the electrolyte, the mass fraction of the compound A is 0.5% to 10%, and the mass fraction of the compound B is 0.1% to 5%.

8. The electrolyte according to any one of claims 1 to 5, characterized in that The additive further comprises at least one of fluorocarbonate and nitrile compound, the mass fraction of the fluorocarbonate is 5% to 35%, and the mass fraction of the nitrile compound is 1% to 7%.

9. The electrolyte according to claim 8, characterized in that The fluorocarbonate comprises at least one of ethylene fluorocarbonate, ethyl methyl fluorocarbonate and diethyl fluorocarbonate; and / or The nitrile compound includes at least one of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, 1,2,3-tri(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tri(cyanoethoxy)pentane.

10. An electrochemical device, characterized in that: The invention comprises a shell, a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9, which are arranged in the shell.

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